Detecting early dental caries and monitoring its dynamic process of damage and repair are challenging tasks with current methods available to dentists. Conventional diagnostic methods rely on subjective clinical criteria with early lesions often going undetected. As a result, many lesions are either undiagnosed until they have progressed to a cavitated state, or lesions are unnecessarily restored despite the potential to arrest and repair the lesion with remineralization methods such as fluoride strategies. Therefore the need exists for new techniques with high sensitivity and specificity for early detection and monitoring of non-cavitated lesions. Recently, various new methods have been developed as potential diagnostic tools. However, these techniques still suffer from subjectivity, high intra- and inter-examiner variability and false positive results. In addition, these techniques require further validation before they are implemented into caries clinical trials and eventually into clinical settings for assessing tooth surface demineralization and remineralization. The objective of this proposal is to validate a new multi-modal technology that combines imaging (optical coherence tomography, OCT) and spectroscopic (Raman spectroscopy, RS) techniques for improved detection and longitudinal assessment of early caries lesions. To achieve this goal, an intra-oral multi-modal probe designed for approximal caries detection will be refined for broader caries screening. The validity of using the multi-modal OCT-RS approach will be validated for assessing tooth surface de-/remineralization at various tooth surfaces and structures. This procedure involves testing the methodology on extracted human teeth and comparing the findings with a gold-standard method (transverse microradiography). Next, several patient volunteer studies will be conducted to validate the technology in vivo for clinical tooth surface assessment. At the end of the four-year project, the validity and utility of this new tool will be demonstrated. The proposed research studies a novel method that involves two light-based technologies for the detection and on-going monitoring of early dental decay. Early identification allows dentists to arrest and reverse the damage using conservative methods such as fluoride treatment, rather than the irreversible cutting and restoration of tooth structure. Better diagnosis and management of dental decay with cost-effective and less invasive methods will improve the patient's oral health and overall general well-being of the individual.